EntityManager 3.2.0GA / jar locking / PersistenceXmlLoader

Jimr · **Joined:** Thu Nov 30, 2006 6:09 pm **Posts:** 9

I am writing this to document two resolutions to a problem I have found while running EntityManager within a servlet container on Windows and the way that PersistenceXmlLoader.java within EntityManager searches for persistence_1_0.xsd (NOT persistence.xml).

This is specific to windows, and its file locking behaviour.

Environment: Windows XP SP2, JDK 1.5.0_05, Hibernate-everything at 3.2.0GA, Tomcat 5.5.12

Problem: When undeploying a webapp that uses EntityManager, the EntityManager.jar within the webapp is locked and cannot be deleted. This results in a failure to undeploy the webapp. If the servlet container (Tomcat) is shut down, the lock is released and the jar can be deleted.

PersistenceXmlLoader.java involvement: This class appears to be involved in searching for persistence_1_0.xsd on the classpath using a url. However it does not set caching to false before doing the configURL.openStream() call. This means that all the jars that it opens get locked by windows.

Root cause: Jar access using a URL with caching enabled. See:
http://forum.springframework.org/archive/index.php/t-19516.html
http://tomcat.apache.org/faq/windows.html#lock

Resolution #1:
Copy persistence_1_0.xsd out of EntityManager.jar, and place it in WEB-INF/classes. This should cause the xml loading code to find it first, and not search any of the jars.

Resolution #2:
Make sure the following code is ran before instantiating the EntityManager (can use ServletContextListener for example):

Code:

    try
   {
      if(System.getProperty("os.name").contains("Windows"))
         new URL("http://This-is-just-to-get-the-URLConnection").openConnection().setDefaultUseCaches(false);
   }
   catch (IOException e)
   {
      e.printStackTrace();
   }

This is a vm-wide setting so it will affect all url connections. Why isn't this code cleaner? See:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4851466
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4405789

I hope this helps anyone else in the same situation!
Maybe the code could also be in EntityManager itself? I'll leave that to the dev team.

Jim

emmanuel · **Posted:** Tue Dec 05, 2006 6:43 pm

http://opensource.atlassian.com/projects/hibernate/browse/EJB-256

I've added in PersistenceXmlLoader.loadURL

Code:

if (configURL != null) {
         URLConnection conn = configURL.openConnection();
         conn.setUseCaches( false ); //avoid JAR locking on Windows and Tomcat
         is = conn.getInputStream();
      }

Let me know if that fixes your issue.

Jimr · **Joined:** Thu Nov 30, 2006 6:09 pm **Posts:** 9

Yes, that will do the trick.

I like the use of setUseCaches() for this particular URLConnection because it avoids having Hibernate affect the entire vm. I used setDefaultUseCaches() simply to avoid modifying the many jars I am using.

Setting caching to false for the URLConnection may have a minor performance hit though, so it wouldn't hurt to profile this change. That is also why I have

Code:

if(System.getProperty("os.name").contains("Windows"))

in my code. I am isolating the change to the OS where the problem occurs.

Jim

emmanuel · **Posted:** Thu Dec 07, 2006 3:39 pm

I don't expect any serious perf penalty since this URL will not be reused beyond Persistent Unit initialization.